Does Endometriosis Show Up on MRI and Fibroids: What to Know

Pelvic pain, heavy periods, and fertility challenges often trigger a work-up for endometriosis or uterine fibroids. Imaging is a key part of that evaluation—but how reliable is MRI, and when is it used? Here’s a clear, evidence-based guide to what MRI can and cannot show for endometriosis and fibroids, how it compares to ultrasound and surgery, and what to expect from the process.

The quick answer

• Endometriosis: MRI can detect certain forms—especially ovarian endometriomas and deep infiltrating endometriosis (DIE)—with good accuracy. However, MRI often misses superficial peritoneal lesions, so a normal MRI does not rule out endometriosis.
• Fibroids (uterine leiomyomas): MRI is excellent for mapping size, number, and location, especially when the uterus is enlarged or anatomy is complex. It helps plan surgery or procedures like uterine fibroid embolization.

Guidelines generally start with pelvic or transvaginal ultrasound. MRI is added when ultrasound is inconclusive, when deep disease is suspected, or for complex surgical planning.

How MRI works for pelvic conditions

Pelvic MRI uses magnetic fields and radio waves to create high-contrast images of soft tissue without radiation. For endometriosis and fibroids, radiologists use sequences that highlight blood products, fibrous tissue, and inflammation. Contrast dye (gadolinium) may be used to better delineate active lesions and enhance mapping, depending on the question being asked.

Does endometriosis show up on MRI?

It depends on the type and location:

• Ovarian endometriomas: These “chocolate cysts” have a characteristic MRI appearance (high signal on T1 and “shading” on T2), and MRI detects them with high sensitivity and specificity. This is one of MRI’s strengths.
• Deep infiltrating endometriosis (DIE): Lesions that invade structures like the uterosacral ligaments, rectovaginal septum, bowel, or bladder are often visible. MRI helps determine how far disease extends and whether nearby organs are affected, guiding surgical planning. Systematic reviews and the American College of Radiology (ACR) note good accuracy for DIE, although performance varies by location.
• Superficial peritoneal endometriosis: These small, surface lesions commonly do not show up on MRI. A normal MRI cannot exclude endometriosis, especially in patients with classic symptoms.

Professional guidance (ACOG, NICE, ACR) emphasizes that imaging supports diagnosis but does not replace clinical judgment. Empiric treatment may be appropriate based on symptoms even if imaging is normal.

Key numbers (what studies show)

• Ovarian endometriomas: MRI typically demonstrates high diagnostic accuracy (often reported in the 90%+ range for sensitivity/specificity).
• DIE (site-dependent): Pooled estimates frequently show sensitivity around 80–90% and specificity around 90% or higher for certain sites (e.g., rectosigmoid, uterosacral ligaments), but results vary based on technique and expertise.

Sources: ACR Appropriateness Criteria on Endometriosis; NICE guideline NG73; ACOG guidance on endometriosis evaluation and management.

How fibroids appear on MRI

MRI is highly effective for fibroid mapping. It shows number, size, and location (submucosal, intramural, subserosal) with excellent soft-tissue contrast. MRI can also identify degeneration (e.g., hyaline, cystic, red degeneration) and differentiate fibroids from other masses. This level of detail helps:

• Plan myomectomy by showing exact locations and relationships.
• Assess candidacy for uterine-sparing procedures like uterine fibroid embolization (UFE) or MR-guided focused ultrasound.
• Distinguish fibroids from adenomyosis (which can coexist and mimic symptoms).

Sources: RadiologyInfo (RSNA/ACR patient resource) on pelvic MRI and fibroid procedures; NIH MedlinePlus/NICHD on uterine fibroids.

MRI vs ultrasound vs laparoscopy

• Ultrasound (US): Usually the first-line test. Transvaginal ultrasound is excellent for identifying fibroids and ovarian cysts, widely available, and cost-effective. Specialized “expert” ultrasound can detect some deep endometriosis, but availability varies.
• MRI: Second-line for complex cases, surgical planning, suspected deep endometriosis, or when US is inconclusive. MRI excels at mapping fibroids and complex pelvic anatomy.
• Laparoscopy: Historically the diagnostic “gold standard” for endometriosis because it allows direct visualization and biopsy. Current guidelines (ACOG, NICE) support a pragmatic approach: consider empiric therapy based on symptoms and noninvasive testing, reserving laparoscopy for persistent symptoms, unclear diagnoses, or when surgery is planned.

When do clinicians order MRI?

• Severe symptoms with suspicion for deep infiltrating endometriosis (bowel, bladder, uterosacral ligaments).
• Preoperative planning for myomectomy, UFE, or endometriosis surgery.
• Discordant or inconclusive ultrasound findings.
• Complex anatomy (very large uterus, prior surgeries, multiple lesions).
• To evaluate adenomyosis or differentiate it from fibroids.

What MRI can miss

• Small, superficial endometriosis implants on the peritoneum.
• Microscopic disease not producing structural change.
• Lesions obscured by motion or suboptimal technique; interpretation also depends on radiologist experience.

Preparing for pelvic MRI and what to expect

• Screening for safety: Tell your team about any implants, metal fragments, or medical devices. Most implants are safe or “conditional,” but they must be checked in advance. Discuss kidney function and allergies if contrast is planned. See FDA and RadiologyInfo resources on MRI safety and gadolinium.
• Day of scan: You’ll lie still in the scanner for 30–60 minutes. Some centers use an antispasmodic to reduce bowel motion. You may receive contrast via IV.
• Comfort tips: If you’re claustrophobic, ask about an open MRI, music, or mild sedation.

Understanding your results

• For endometriosis: Findings might include endometriomas, nodules along the uterosacral ligaments, rectovaginal septum, bladder, or bowel involvement. A normal MRI does not exclude disease—your clinician will integrate symptoms, exam, and other tests.
• For fibroids: Reports detail number, size, and location, and note degeneration or atypical features. This guides whether medical therapy, surgery, UFE, or watchful waiting is appropriate.

When both conditions are suspected

Endometriosis and fibroids can coexist and share symptoms: pelvic pain, heavy bleeding, painful intercourse, and fertility challenges. MRI can simultaneously map fibroids and assess for deep endometriosis and adenomyosis, helping personalize treatment. Your care plan may involve medical therapy (e.g., hormonal options), surgery, or interventional radiology, tailored to your goals (pain relief, fertility preservation, uterine-sparing approaches).

Practical takeaways

• Start with a detailed symptom history, pelvic exam, and ultrasound.
• Use MRI when deep disease is suspected, ultrasound is inconclusive, or surgical planning is needed.
• Remember: a normal MRI does not rule out endometriosis, especially superficial disease.
• For fibroids, MRI offers the best map for complex cases and procedure planning.
• Discuss results and next steps with a gynecologist experienced in endometriosis/fibroid care.

Trusted resources

• ACOG: Endometriosis and Uterine Fibroids overviews and practice guidance: acog.org/womens-health
• NICE Guideline NG73: Endometriosis diagnosis and management: nice.org.uk/guidance/ng73
• ACR Appropriateness Criteria (Endometriosis; Chronic Pelvic Pain): acsearch.acr.org/list
• NIH/NICHD on Endometriosis: nichd.nih.gov
• NIH MedlinePlus on Uterine Fibroids: medlineplus.gov/uterinefibroids.html
• RadiologyInfo (RSNA/ACR): Pelvic MRI and fibroid procedures/UFE: radiologyinfo.org
• FDA on MRI safety and gadolinium-based contrast agents: fda.gov

This article is informational and not a substitute for medical advice. If you have pelvic pain, heavy periods, or fertility concerns, consult a healthcare professional for individualized evaluation.